Interpretive Summary: Rebuds (Cercis species) are small trees or shrubs that are prized in the landscape for their early spring bloom. As the demand for new cultivars increases, breeders need tools to evaluate the genetic diversity among the 11 species in order to identify and create new hybrids. We have tested a set of previously developed molecular markers in 50 diverse Cercis species and cultivars. We found that these markers can readily differentiate the taxa, and that they provide valuable information on genetic relationships among taxa as well as clues to origins. The markers will also be useful in cultivar identification and in germplasm management. These results will be useful to breeders, curators, and nursery growers.

Technical Abstract:
The genus Cercis contains 11 recognized species. Althought morphological characters are generally useful for distinguishing among the species, molecular data can be helpful to resolve taxonomic or parentage issues, as well as to examine associations between morphological variation and environment. Three species have been used in ornamental plant breeding in the U.S. including three botanical varieties of C. canadensis from North America, and two Asian species, C. chingii and C. chinensis. We sampled fifty-one accessions comprising eight species of Cercis and a closely related species, Bauhinia faberi. Sixty-eight polymorphic SSRs were used to assess genetic relationships between species and cultivars. The number of alleles detected for all samples ranged from 2 to 20 and included 22 loci (32%) that detected 10 or more alleles. Observed heterozygosity ranged from 0.00 to 0.61 with a mean of 0.27, whereas expected heterozygosity ranged from 0.06 to 0.92 with a mean of 0.61. Average polymorphic information content (PIC) was 0.57 and values ranged from 0.06 to 0.91 with 44 loci = 0.50. Cross species transfer within Cercis was extremely high, with 55 loci that amplified at 100%. Results support previously reported phylogenetic relationships of the North American and western Eurasian species and indicate suitability of these markers for mapping studies involving C. canadensis and C. chinensis. Results also support known pedigrees from ornamental tree breeding programs for the widely cultivated C. canadensis and C. chinensis species, which comprised the majority of the samples analyzed.